The use of biodegradable materials had increased over the past years due to the environmentally beneficial properties of such materials. Such materials are now commonly used in the manufacture of a wide range of products, including various types of plastic bags and other forms of packaging. In response to the demand for more environmentally friendly packaging materials, a number of new biopolymers have been developed that have been shown to biodegrade when discarded into the environment.
Examples of such polymers include polyesteramide (PEA), modified polyethylene terephthalate (PET), biopolymers based on polylactic acid (PLA), polyhydroxyalkanoates (PHA), which include polyhydroxybutyrate (PHB), polyhydroxyvalerate (PHV) and polyhydroxybutyrate-hydroxyvalerate copolymer (PHBV), and poly (epsilon-caprolactone) (PCL).
Each of the foregoing biopolymers has unique properties, benefits and weaknesses. For example, modified PET, PEA, PHB and PLA tend to be strong but are also quite rigid or even brittle. This makes them poor candidates when flexible sheets are desired, such as for use in making wraps, bags and other packaging materials requiring good bend and folding capability.
On the other hand, biopolymers such as PHBV and polybutylene adipate terphtalate (PBAT) are many times more flexible than the biopolymers discussed above, but have relatively low melting points so that they tend to be self-adhering and unstable when newly processed and/or exposed to heat.
Further, due to the limited number of biodegradable polymers, it is often difficult, or even impossible, to identify a single polymer or copolymer that meets all, or even most, of the desired performance criteria for a given application. For these and other reasons, biodegradable polymers are not as widely used in the area of food packaging materials, particularly in the field of liquid receptacles, as desired for ecological reasons.
In addition, the biodegradable sheets known today are mostly opaque, having low light transmittance and high haze. Further, the known biodegradable sheets either do not include barrier layers or include amounts and types of barrier layers that cause the sheets to be generally highly permeable to gases, having both a high oxygen transmission rate (OTR) and a high water vapor transmission rate (WVTR), and thus they cannot serve as long term food or drink receptacles. Additionally, the physical strength of known biodegradable sheets, measured by parameters such as stress at maximum load, strain at break and Young's Modulus, is lacking and, therefore, such sheets are deficient when used as packaging, particularly for packaging liquids.
International Patent Publication No. WO 2011/158240 to the assignee of the present application discloses biodegradable sheets and an array of separable pouches for liquids.
International Patent Publication No. WO 2013/088443 to the assignee of the present application discloses biodegradable sheets comprising a gas barrier material, which is a nanoclay and/or polyvinyl alcohol.
International Patent Publication No. WO 2013/186778 to the assignee of the present application discloses biodegradable sheets comprising at least one layer which comprises a biodegradable polymer and surface treated nanoclay particles and/or polyvinyl alcohol (PVOH) grafted with a crosslinker and polybutylene succinate (PBS) or polybutylene succinate adipate (PBSA).
International Patent Publication No. WO2015/059709 to the assignee of the present application discloses biodegradable sheets comprising a contact layer.
Although there have been some advances in the field of biodegradable packaging, there remains a need for flexible and biodegradable packaging with improved impermeability to water vapor and/or oxygen.